1. Field of the Invention
The present invention relates to a Micro Electro Mechanical System (MEMS) switch, such as Radio Frequency (RF) switch, fabricated using a MEMS technique, and in particular to a MEMS switch using a pneumatic pressure, and a method of fabricating the same.
2. Description of the Related Art
In general, a MEMS switch, such as an RF switch, that is configured using a MEMS technique, includes a switch pad in the shape of a bridge or a cantilever, which is driven by a driving electrode. The switch pad is elastically supported on a substrate by a supporting spring. The driving electrode is formed opposite to the switch pad on the substrate so as to drive the switch pad.
In such a conventional MEMS switch, a driving voltage applied to the driving electrode depends on an elastic modulus of the supporting spring, which enables the switch, pad to come into contact with or move away from a signal line under the influence of an electrostatic force, thereby switching signal flow. Accordingly, in order to reduce the driving voltage applied to the driving electrode and switch the signal flow at a high speed, the supporting spring is usually designed to have a low elastic modulus below a certain level. As a result, the conventional MEMS switch presents a first problem in that the elastic force of the supporting spring which maintains switching contacts of the switch pad to move away from switching ends of the signal line weakens, thereby allowing the switch pad to be easily vibrated with a small external force, and a second problem in that a jointed portion between the supporting spring and the switch pad weakens, thereby resulting in fabrication defects.
In order to address these problems, a new concept of MEMS switches has been developed of removing a mechanism in which the switch pad repeats mechanical deformation and restoration through the supporting spring while being operated. These MEMS switches are disclosed in U.S. Pat. Nos. 6,294,847, 6,143,997 and 6,489,857.
A bistable micro-electromechanical switch of U.S. Pat. No. 6,294,847 uses two parallel plate capacitors that drive a dielectric beam attached to a movable transmission line segment. The bistable micro-electromechanical switch, however, has a disadvantage that in order to overcome a sticking problem, such as friction or collision of the movable transmission line segments generated while the dielectric beam is driven along with the movable transmission line segment, a relatively large of driving force is required. If a driving voltage applied to the capacitors is increased to increase the driving force, power consumption is not only increased, but also it is difficult for the bistable micro-electromechanical switch to be employed to a system or module such as a handset, an antenna tuner, a transmitting/receiving set, and a phased array antenna, which requires a MEMS switch drivable with a low driving voltage.
MEMS switches of U.S. Pat. Nos. 6,143,997 and 6,489,857 include a conductive pad or a movable body drivable by top and bottom driving electrodes or first and second field plates, and a bracket or a guidepost to guide the conductive pad or the movable body to go constantly up and down. However, since electrical connection to transmission lines, that is, signal flow, is switched by the conductive pad or the movable body which is guided along the bracket or the guidepost, there can arise a problem in that the electrical connection is cut off, or weakens. Further, the MEMS switches can arise a problem in that the conductive pad or the movable body is jammed due to fabrication tolerance or error between the bracket or the guidepost and a receiving opening of the conductive pad or the movable body while it is moving up and down, thereby deteriorating reliability in operation. However, to address these problems, if a driving voltage applied to the top and bottom driving electrodes or the first and the second field plates is increased, power consumption is not only increased, but also it is difficult for the MEMS switches to be employed to a system or module which is driven with a low driving voltage, similar to the bistable micro-electromechanical switch of U.S. Pat. No. 6,294,847.
Accordingly, there is required a new MEMS switch that can not only be stably operated, but also driven with a low driving voltage which satisfies a driving voltage condition of the system or module to be used without employing the supporting spring which should be designed to have the low elastic modulus below the certain level.